Re: [opensuse] apparently Suse-Linux can't properly use quadcore processor???

On Mon, Nov 01, 2010 at 11:16:16AM -0400, Larry Stotler wrote:

On Sun, Oct 31, 2010 at 3:59 PM, Oliver Kullmann wrote:

...

I'm here experiencing an alarming problem (not just KDE or so, but the kernel): I have a laptop with a quadcore i5 processor, but the system doesn't want to use it! That's not good, since I rely on doing computational experiments with my laptop, and, of course, I purchased the quadcore laptop to do exactly that.

You are aware that a mobile Core i5 is actually a dual core processor with hyper threading?

As I said, after the (strange) "warming up phase" is over (for unknown reasons), it behaves exactly as having four independent processors (for the jobs I run, I can run 4 of them at the same speed as a single job).

http://en.wikipedia.org/wiki/List_of_Intel_Core_i5_microprocessors

Only 3 of the desktop Core i5's are true quad core, and they have hyperthreading disabled.

The Linux kernel knows that the chip is actually a dual core with hyperthreading vs a true quad core, and will therefore schedule most tasks to work on the 2 actual cores, not the virtual cores. Win2k and XP had problems where they would use the virtual core and main core of the first chip of a dual proc system instead of the real 2 cores and performance would suffer.

Perhaps that is the assumption at the beginning, and then it figures out differently?

While the new Core ix series implementation of hyperthreading is better than what was on the P4s, it's still not a true additional core. Further, there are other issues:

"Also, moving an application to two threads on a single SMT-enabled core will increase cache-thrashing by 42%, whereas it will decrease by 37% when moving to two cores."

That's from this article:

http://www.theinquirer.net/inquirer/news/1037948/arm-fan-hyperthreading

Hyperthreading can be a nice boost, but a Core i7 with true quad core would be a better choice if you need 4 cores.

I can't complain for what I'm running (some form of scientific computation, but not much numerics). Thanks Oliver -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org